PHOTOSYNTHESIS IN THICK CYANOBACTERIAL FILMS - A COMPARISON OF ANNUAL AND PERENNIAL ANTARCTIC MAT COMMUNITIES

Annual and perennial cyanobacterial mats from streams on Signy Island, Antarctica, show similar areal concentrations of chlorophyll-a and areal rates of photosynthesis. Maximum rates of photosynthesis were temperature dependant over the range 0-14 C, with a Q10 of approximately 2.5. Rates of photosynthesis per unit chlorophyll-a were comparable to other Antarctic mat communities but low compared to phytoplankton from upstream lakes. Areal rates of photosynthesis were however much higher than for phytoplankton. Low chlorophyll-specific rates of photosynthesis are interpreted as the effect of self shading within the mats. It is hypothesised that these mats rapidly attenuate incoming radiation and that photosynthesis in most of the mat is effectively light-limited. This situation is likely to occur in all thick periphyton films.